for Disease Control and Prevention. 2003. Second National
Report on Human Exposure to Environmental Chemicals. NCEH
Pub. No. 02-0716.
sampling of press coverage:
Francisco Chronicle op-ed
the largest and most extensive survey of American body burdens of
environmental chemicals ever undertaken, the Centers for Disease
Control found widespread low-level contamination in a random sample
of Americans in 1999-2000.
good news is that steps taken to reduce exposures are having
a positive effect, and that current levels of most
of the chemicals measured are beneath those known to cause harm.
chemicals are present at levels associated with health effects.
Among the most troubling findings are:
of an earlier, smaller
CDC study that documented widespread exposure to phthalates.
of phthalates are highest in children and women of reproductive
age, creating the potential for developmental effects on the
fetus and children.
to 10% of American women carry mercury
concentrations near the level considered to put fetal development
at risk to neurological damage.
this is the most ambitious body burden survey ever undertaken,
it measured only 116 of the thousands of chemicals in modern
use. Many of those thousands are unlikely to have health effects.
But the survey left out many compounds, like
arsenic, bisphenol A and the polybrominated diphenyl ethers,
now known to be biologically active at low
levels and known to interfere, in animals, with important
developmental processes. These compounds are used in processes
and products that certainly create human exposures.
health implications of most of the exposures the CDC found are
largely unknown, because few of the chemicals measured have thorough
toxicological profiles. Indeed most have received little study,
particularly of developmental effects, which are likely to be
the most sensitive to low level exposures. None have been
studied thoroughly for health impacts in the mixtures
in which they were found.
did they do? Scientists and health professionals collaborating
with the CDC obtained blood and urine samples from subjects participating
in the National
Health and Nutrition Examination Survey (NHANES) during 1999
and 2000. This survey is one of a series conducted by the CDC to
track the health and nutritional status of people living in the
US. These samples were then analyzed by CDC chemists to determine
blood or urine levels of 116 chemicals.
of which chemicals to analyze was based on several considerations,
including potential importance to health, cost and availability
of suitable assays. No standardized analytical techniques have been
developed for many compounds of potential interest.
compounds measured included an array of metals like lead, cadmium,
colbalt and uranium, organochlorine pesticides like DDT, metabolites
of organophosphate pesticides, other modern use pesticides including
atrazine and chemicals like dioxins and furans produced as byproducts
of industrial processes and incineration. The pesticide measurements
usually focused on metabolites
of the compounds rather than the pesticide itself.
did they find? For several contaminants for which historical
data are available, body burdens are down significantly. For example,
the percentage of children with blood lead levels above 10 µg/dL,
the level at which current
data indicate children suffer neurological impacts, has been
cut in half since the last survey in 1991-94.
and PCB levels are also down markedly. Hexachlorobenzene, another
organochlorine pesticide banned from use in the US in 1984, was
detected in only 0.6% of people sampled. Dioxins, furans and co-planar
PCBs were not detectable in most people measured, although the small
amount of blood sampled from each person and the detection limits
of the analytical techniques limits the conclusions that can be
drawn from this dioxin result.
these declines reflect the impacts of strong protective measures
put in place to restrict or eliminate use of the compound.
traces of some agricultural pesticides were noticably higher in
Mexican Americans than in African Americans or non-Hispanic whites.
This was found for several compounds now banned in the US, for example
DDT and hexachlorocylclohexane, as well at least one current-use
The average DDE
level found in Mexican Americans was 674 ng/g
compared to 295 ng/g and 217 ng/g in African Americans and non-Hispanic
most of the chemicals measured, too few historical data exist to
allow any assessment of trends. This study will serve as an important
benchmark against which to measure future progress. Residential
uses of chlorpyrifos,
for example, ended in 2001; parathion use will be banned in 2003.
The next CDC body burden assessment should find reduced levels.
trends on mercury are not available, although ongoing large-scale
liberation of mercury into the environment (particularly via combustion
of coal) and incorporation thereafter into the food chain (particularly
fish) would indicate that body burdens are rising (see the United
Mercury Assessment, January 2003). Average levels observed in
American women and children are, respectively, approximately 1/50th
and 1/100th the lowest level known to cause neurodevelopmental problems
(58 µg/L). Approximately 10% of US women, however, carry mercury
at blood concentrations much closer to this level. Over time, the
recurring pattern in studies of neurodevelopmental risks is for
new research to reveal greater sensitivity, as research designs
become more sophisticated. Hence the gap between that concentration
known to cause effects and levels experienced by many women is not
on phthalates confirmed and extended the CDC's
2000 finding that virtually all Americans carry a body burden
of these plasticizers. As with the previous work, phthalate contamination
levels were determined by measuring urinary metabolites of the phthalates,
not the parent compound itself. In this survey, different types
of phthalates showed different patterns.
example, the metabolite of dibutyl phthalate (commonly used in cosmetics)
reaches higher levels in women than in men; is higher in African
Americans than in non-Hispanic whites; and is higher in children
than in adults.
metabolite of di-2-ethylhexyl phthalate (used as a plasticizer in
polyvinyl chloride and thus common in toys, flexible tubing, shower
curtains, etc.) is also higher in children than adults. The FDA
has recently recommended that DEHP be removed from medical equipment
that might create exposures for fetal and infant males, and the
European Union has banned the use of DEHP in toys intended for young
November 2002 the EU also mandated removal of dibutyl phthalate
and di-2-ethylhexyl phthalate from cosmetics.
phthalate levels reported in this study by the CDC are very similar
in magnitude to those found by a
Harvard study published in 2003 to be associated with sperm
damage in men living in the Boston area.
does it mean? This study offers new insights into patterns
of contamination of people living in America. Its clearest message
is that public decisions to reduce exposures can yield dramatically
positive results. Lead and DDT are two prime examples.
report brings additional value by providing a baseline against which
future measurements can be compared, allowing trends to be tracked,
and by providing health professionals a snapshot of typical contamination
patterns. This may be helpful in diagnostic work because it will
be a benchmark against which to compare contamination burdens of
contributions are important, but equally important is the
spotlight that this report shines on ignorance. Too little
information is available on the human health impacts of the vast
majority of chemicals surveyed, one-by-one and especially their
effects in complex mixtures. Indeed, too few of the thousands of
potential chemicals that are likely to be part of the human body
burden were sampled by this study.
evidence, mostly from animal experiments, that low-level exposures
to biologically-active contaminants are plausibly linked to a range
of human health effects, this state of ignorance is unacceptable.
the absence of dramatically stronger, scientifically-based assurances
of safety, efforts to reduce exposures to biologically-active
compounds should be redoubled. Those assurances now rest
on the absence of data—the requisite studies simply haven't
been done—instead of on carefully conducted studies demonstrating